2013; Walton 2013; Walton et al. Working off-campus? Medium kamacite lamellae sized at 0.5 to 1.3mm. 1996, 2000; Liu et al. 1969; Xie et al. 8. 2000; Mang et al. Assessment of the probability of microbial contamination for sample return from Martian moons I: Departure of microbes from Martian surface. 1996, 2003; Tomioka and Fujino 1997; Langenhorst and Poirier 2000; El Goresy et al. As mentioned in the Issues Related to the Current Shock Classification of Meteorites section, the shock pressures inferred from high‐pressure phases are significantly lower than those concluded from the S6 shock classification, and slightly to moderately lower than the shock pressures deduced from the shock effects in the main rock‐forming minerals. After decompression to zero GPa, the temperature of the whole rock needs to be lower than the temperature at which high‐pressure phases become unstable at low pressure. Because pore space collapse occurs at pressures <1 GPa, very high shock temperatures can be achieved at low shock pressures in porous rocks (Meyer et al. Stones with chondrules, they are rich in plagioclase, pyroxene and olivine. Thus, high‐pressure phases in L6 chondrites may reasonably reflect the conditions during one extraordinary impact event (Chen et al. These are the destructive and constructive effects of shock metamorphism reproduced and pressure calibrated by microsecond shock recovery and static pressure experiments, respectively. This is of fundamental relevance to understand that the destructive shock effects observed in the rock‐forming minerals are indicative of higher pressures than those deduced from the high‐pressure phase assemblages in melt zones of meteorites. Volatile rich with sharply defined minichondrules. The current shock classification scheme for ordinary (Stöffler et al. For example, the preservation of bridgmanite in the Tenham L6 chondrite meteorite (Tschauner et al. A large number of L chondrites experienced radiometric age resetting at ~480 Ma ago (Haymann 1967; Bogard 1995; Korochantseva et al. The nature of the L chondrite parent body's disruption as deduced from high‐pressure phases in the Sixiangkou L6 chondrite. According to Stöffler et al. To ask questions, report problems or for general inquiries, see Contact. Fraknoi, et al. This could be two materials of different compressibility or material shocked to two different pressures at which the compressibility of the material substantially differs. 2011), and (5) to study the collisional history of the planetary system orbiting the Sun (e.g., Beck et al. Most of the high‐pressure phases form by kinetically controlled processes requiring very high temperatures (Xie and Sharp 2007). Copyright ©1999-2007, Astrodigital, http://www.astrodigital.org. It is a carbonaceous meteorite containing a complex, tar-like substance. 1992) and enstatite (Rubin et al. The stony meteorites are more common but harder to identify, often requiring isotopic analysis to be sure. 2005a); a time span apparently sufficient to cause a significant loss of radiogenic 4He (Schwenzer et al. This is why classification of meteorites by … Note that not all meteorites fit into the categories listed below. Please check your email for instructions on resetting your password. The latter observation will be addressed below. 5a). The shock‐induced brown staining of olivine can subsequently be bleached by intense thermal metamorphism near local zones of hot shock melt. However, as high‐pressure phases are recognized in an ever increasing number of achondritic meteorites (e.g., Lipschutz 1964; El Goresy et al. Destructive shock effects in other minerals diagnostic for shock pressures in excess of 45–60 GPa can be added to the list of diagnostic shock features. The diagnostic criteria for S6 include olivine with strong mosaicism, in part smoothed by recrystallization and shock‐induced brown staining, a feature which is not affected by mild annealing. 2006; Ott 2007 and references therein). This thermally induced age resetting is apparently related to a major disruption event of the L chondrite parent body at that time which is coincident with a large number of fossil meteorites recovered from mid Ordovician limestones (Schmitz et al.

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